Method for inerting a line carrying an explosive gas and system with a line carrying an explosive gas

Abstract

The invention relates to a method for inerting a line (1) of a system (2), for example an electrolysis system or a fuel cell system, which carries an explosive gas, wherein a liquid enriched with an inert gas, for example water, in particular deionized water, is used for inerting, with which the line (1) is purged. The invention further relates to a system (2), in particular an electrolysis system or a fuel cell system, with a line (1) which carries an explosive gas.

Description

The present invention relates to a method for inerting a conduit carrying an explosive gas, for example hydrogen. Such a line is found, for example, in an electrolysis system or in a fuel cell system. The invention furthermore relates to a system, in particular an electrolysis system or a fuel cell system, having a line which conducts an explosive gas.Preferred applications of the invention are electrolysis systems for generating hydrogen or fuel cell systems which use hydrogen as process gas.Prior ArtHydrogen has a broad explosion range, that is to say that even small amounts of hydrogen in air and small amounts of air or oxygen in hydrogen can lead to an explosion when a (ignition) spark occurs. In systems which have hydrogen-carrying lines, the lines are therefore flushed or inertized with an inert gas, for example with nitrogen, in idle and / or standby times, in order in this way to avoid dangerous hydrogen accumulations.Purging with inert gas at system idle or standby times results in dilution of the hydrogen, thus minimizing the risk of explosion. If the system is then started up again, the inert gas introduced for inerting must first be completely removed, since it leads to contamination of the hydrogen and thus of the product gas or process gas. Depending on the requirements, this must then be discarded.An alternative approach to inertizing conduits involves the use of a liquid instead of inert gas. The liquid can be, for example, deionized water, also called DI water. The use of DI water is particularly suitable for inertizing lines in electrolysis systems which use DI water as electrolyte. This means that DI water is present and does not have to be stored separately. The process-related presence of DI water in the system also excludes contamination of the product gas.Inerting a line with a liquid can, however, prove to be problematic if the line has branches, discharges and / or connections which lead to the formation of hollow spaces and / or blind tube regions. This is because the explosive gas can collect in the latter, so that it cannot be displaced by the liquid flow during flushing. For forming such cavities, it may occur in particular below valves, for example safety valves, and / or in line sections with a local maximum. Depending on the size of the cavities, critical gas quantities can accumulate there, which form an explosive gas mixture in conjunction with air, which reaches the cavity via a leak, for example.The present invention is concerned with the object of eliminating the above-mentioned disadvantages in inertizing a line carrying an explosive gas. In particular, the intention is to keep contaminants in the gas to a minimum and to prevent critical gas accumulations in cavities in the line.To achieve the object, the method having the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the dependent claims. Furthermore, a system, in particular an electrolysis system or a fuel cell system, with a line carrying an explosive gas is specified.Disclosure of the InventionA method for inertizing a line of a system, for example an electrolysis system or a fuel cell system, which line conducts an explosive gas is proposed. In the method, an inert gas-enriched liquid is used for inerting, with which the line is flushed. The liquid enriched with inert gas displaces the gas present in the line during flushing, so that the line is rendered inert. If the line has a gas-filled cavity into which the liquid cannot pass, the cavity can be inertized with the aid of the inert gas with which the liquid has been previously enriched. This is because the inert gas mixes with the explosive gas present in the cavity, so that the latter is diluted. The risk of explosion is thereby minimized.The amount of inert gas used in the proposed method is small, in particular in comparison with inertization with pure inert gas. If the explosive gas is a product gas, for example hydrogen, this is hardly contaminated by the small amounts of inert gas. This means that after inerting, only small amounts of product gas have to be discarded.The liquid enriched with inert gas can be water, in particular DI water. This is advantageous in particular if the system uses water or DI water as a result of the process, for example as electrolyte. The water or DI water is then already present and does not have to be stored separately. In addition, the liquid cannot then lead to contamination of the product or process gas.According to a preferred embodiment of the invention, the liquid is enriched with nitrogen as inert gas. Nitrogen has already proven its worth as inert gas for inerting.Preferably, the liquid is enriched until saturated with inert gas. That is, a maximum amount of inert gas is dissolved in the liquid. This facilitates the separation of the inert gas from the liquid.Furthermore, the liquid enriched with the inert gas is preferably introduced under pressure into the line and actively or passively expanded in the line. Releasing the inert gas-enriched liquid promotes outgassing of the inert gas. The expansion can be actively effected by a targeted pressure reduction or passively by method-induced pressure fluctuations. The outgassed inert gas collects in the cavity of the line and displaces or at least dilutes the explosive gas present there.Alternatively or additionally, it is proposed that the liquid enriched with the inert gas is actively or passively heated in the line, so that outgassing of the inert gas is promoted. For example, the liquid enriched with inert gas can be introduced "cold" into the line, so that it is heated in the line by the ambient and / or process heat. Alternatively, the liquid enriched with inert gas can also be actively heated, for example with the aid of an electric heater. Outgassing of the inert gas can likewise be initiated by changing the temperature.In a further development of the invention, it is proposed that the compressibility of the liquid introduced into the line and enriched with the inert gas is determined with the aid of at least one pressure sensor. The gas proportion can be determined via the compressibility, since the gas or gas mixture present in the line can be compressed to a greater extent than the liquid. The gas fraction in turn makes it possible to conclude gas-filled cavities in the line.Preferably, the line is rendered inert with the liquid enriched with the inert gas when the system is at a standstill, during standby operation of the system and / or during black-out of the system, i.e. in the event of a spontaneous interruption of the power supply of the system. This ensures that inerting does not interfere with normal operation. In addition, critical gas accumulations in standstill times are avoided, so that the safety of the system is increased when it is out of operation.Furthermore, after inerting, preferably when the system is restarted, the line is flushed with inert gas-free liquid. The line is freed of inert gas by the flushing, so that contamination of the product gas or process gas by foreign gas is avoided.Furthermore, a system, in particular an electrolysis system or a fuel cell system, having a line carrying an explosive gas and a container in which a liquid enriched with inert gas, for example water, in particular DI water, is accommodated is proposed. The line is connected directly or indirectly to the container. This means that the liquid enriched with the inert gas can be introduced into the line or the line can be rendered inert by the method according to the invention described above.The proposed system is therefore suitable in particular for carrying out the method according to the invention described above, with the result that the same advantages can be achieved. In particular, critical gas accumulations in cavities of the line can be avoided, so that the safety of the system increases. Furthermore, the product or process gas can be kept largely free of impurities.According to a preferred embodiment of the invention, the line runs at least in sections through an electrolysis stack or a fuel cell stack. In this embodiment of the system, the stack can be rendered inert at the same time when inerting the line.The invention and its advantages are explained in more detail below with reference to the attached drawings. This shows a schematic illustration of a system according to the invention, in the present case an electrolysis system.DETAILED DESCRIPTION OF THE DRAWINGThe system 2 according to the invention illustrated in the figure, which is designed in the present case as an electrolysis system, comprises an electrolysis stack 4, to which DI water is supplied as electrolyte during normal operation. This is broken down into hydrogen and oxygen in the electrolysis cells of the electrolysis stack 4 in an electrochemical reaction. The oxygen is conducted together with residual water on the anode side out of the electrolysis stack 4. The hydrogen occurs on the cathode side and is transported away via a line 1, optionally together with residual water.In the present case, a valve 6 is arranged on the line 1. The connection of the valve 6 to the line 1 can be established via a T-piece. This means that a connection branches off from the line 1, at the end of which connection the valve 6 is arranged. The valve 6 can be, in particular, a safety valve, by means of which hydrogen can be discharged in a controlled manner. The valve 6 is therefore preferably arranged above the line 1. The connection of the valve 6 to the line 1 results in the formation of a gas-filled cavity 5 above the line 1.In order to avoid critical accumulations of hydrogen in the line 1 during standstill or standby phases, the latter is flushed or rendered inert beforehand. If pure inert gas, such as nitrogen, is used for inerting, it must be completely removed from the line 1 before the system 2 is restarted, which is usually done with the aid of the product gas generated. This must then be discarded, since it is contaminated by inert gas, until all inert gas has finally been displaced from the line 1. This is uneconomical.Alternatively, a liquid, for example water, in particular DI water, can therefore be used for inertizing the line 1. On the one hand, DI water is already present and does not have to be stored separately. On the other hand, the product gas cannot be contaminated as a result. During rinsing with pure water or DI water, hydrogen present in the cavity 5 cannot be displaced by the liquid flow, so that a critical accumulation of hydrogen can occur there.The method according to the invention therefore uses a liquid enriched with inert gas, for example nitrogen, for example DI water, for flushing or inertizing the line 1. This is held in a container 3 which can be filled with DI water via a DI water reservoir (not shown) of the system 2. In the container 3, the DI water can then be enriched with inert gas.To make the line 1 inert, liquid enriched with inert gas is then introduced from the container 3 into the line 1. By means of lowering the pressure and / or heating the liquid, the outgassing of the inert gas in the line 1 can be initiated, so that the inert gas rises into the cavity 5 and dilutes the hydrogen present there. Since in the present case the line 1 runs in sections through the electrolysis stack 4, the electrolysis stack 4 can be rendered inert at the same time.Before the system 2 is restarted, the line 1 is flushed with pure water or DI water, so that the liquid enriched with inert gas is discharged.

Claims

Method for inerting a line (1) carrying an explosive gas of a system (2), for example an electrolysis system or a fuel cell system, wherein a liquid enriched with an inert gas, for example water, in particular DI water, is used for inerting, with which the line (1) is flushed.Method according to claim 1, characterised in that the liquid is enriched with nitrogen as inert gas.Method according to claim 1 or 2, characterised in that the liquid is enriched until saturated with inert gas.Method according to one of the preceding claims, characterized in that the liquid enriched with the inert gas is introduced under pressure into the line (1) and is actively or passively expanded in the line (1), so that outgassing of the inert gas is promoted.Method according to one of the preceding claims, characterized in that the liquid enriched with the inert gas in the line (1) is actively or passively heated, so that outgassing of the inert gas is promoted.Method according to one of the preceding claims, characterized in that the compressibility of the liquid introduced into the line (1) and enriched with the inert gas is determined with the aid of at least one pressure sensor.Method according to one of the preceding claims, characterized in that the line (1) is rendered inert with the liquid enriched with the inert gas when the system (2) is at a standstill, during standby operation of the system (2) and / or when the system (2) is black-out.Method according to one of the preceding claims, characterized in that after inerting, preferably when the system (2) is restarted, the line (1) is flushed with inert gas-free liquid.System (2), in particular an electrolysis system or fuel cell system, having a line (1) carrying an explosive gas and a container (3) in which a liquid enriched with inert gas, for example water, in particular DI water, is accommodated, wherein the line (1) is connected directly or indirectly to the container (3).System (2) according to Claim 9, characterized in that the line (1) runs at least in sections through an electrolysis stack (4) or a fuel cell stack.

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